Highly agile aircraft, such as military aircraft, move at very high speeds. Without technical components that regulate the flight attitude and support the pilots so that they can react to changes with a short reaction time, it is almost impossible to allow stable and ecological flight. For this purpose, flight attitude parameters and environmental parameters are constantly determined by avionics components during flight, and converted by the flight control system, together with the control parameters input by the pilot, into regulation parameters, or displayed on display devices in the cockpit, in processed form. For flight support, strict time requirements are set for the avionics components and, in particular, for the network of different avionics, in particular with regard to the latency and cycle times in the regulation circuit when querying and distributing measurement variables and control parameters within the flight control system.
An example of a network of avionics components that forms a flight control system can be a GPS system, which, together with the air data (pressures, temperatures, and angles) and different inertia sensors constantly calculates the new setting variables for the different actuators, on the basis of the control parameters input by the pilot into the evaluation computers of the flight control system. Other examples are signal networking in a radar system, control of the landing gear, or also a distributed air conditioning device for the cabin with its distributed sensors or actuators for regulating temperature and pressure.
This high requirement for the response behavior of the avionics components, as described, which is connected with a very rapid response time or reaction time of the individual avionics components, is summarized with the term real-time capability. Systems that meet specific time requirements, particularly that guarantee a response within a specific period of time after a command or a message is issued, are referred to as real-time systems or real-time-capable systems.
As already described, avionics systems can be distributed real-time systems, the components of which are positioned in different locations of an aircraft. Because of the installation of the components in different locations, a network or a transmission medium is required in order to join the avionics components into an overall system. Because of increased robustness requirements, particularly with regard to the physical layer of a network protocol when used in aircraft construction, it is generally not possible to use standard network components, which usually provide for collisions in their concepts, because of the simpler management and simpler design of the network, and thereby do not make the behavior of the overall system deterministic.
However, the production costs of standard network components can be lower, because of significantly higher unit numbers and lower real-time requirements, than those of network components to be used in avionics systems to ensure real-time behavior, and, in particular, their physical layer. It would be desirable, for example, to use Ethernet components for transmission. However, an infrastructure based on Ethernet IEEE 802.3 (Institute of Electrical and Electronics Engineers) specifically provides for collisions during joint network access of different components. Ethernet is based primarily on correcting collisions instead of providing for avoiding collisions.
Network systems that can adhere to the determinism that is demanded for avionics systems, on the physical layer and on higher layers, are, for example, the hardwired MILBUS protocol, the EFABUS (European Fighter Aircraft Bus Protocol) protocol, or the EFEx (EFABus Express) protocol on the basis of a glass fiber network.
Aside from the high costs, the network infrastructures used for avionics components have the disadvantage that they are too slow for some future concepts of new avionics applications or possible future avionics applications. For example, the MIL-STD-1553B protocol may be able to deliver a transmission rate of 1 Mbit/s, which appears “slow” in comparison with other commercial networks, but it is nevertheless always still preferred because of the high level of data security and the determinism.
From the article by Wang et al. “A Hard Real-Time Communication Control Protocol Based on the Ethernet,” Proceedings 7th Australasian Conference on parallel and Real-Time Systems (Part 2000), pages 161 to 170, Sydney, Australia, November 2000, Springer Verlag, ISBN 962-430-134-4, it is known to operate an Ethernet-based communication protocol, called the Real-Time Communication Control (RTCC) protocol, on an Ethernet MAC (Medium Access Control) protocol.
The article by A. Mifdaoui, et al., “Real-Time characteristics of Switched Ethernet for “1553B”-Embedded Applications: Simulation and Analysis,” 1-4244-0840-7/07, IEEE 2007, analyzes real-time traffic by analogy to the MIL-STD-1553B databus in a military aircraft, where the traffic shaping methods First-Come First-Served (FCFS), Static Priority (SP), and Weighted Fair Queueing (WFQ) are utilized.
It is possible that there is a demand for determinism in communication on the part of a large number of existing avionics applications.